A new survey suggests 16% of us don’t want to receive a Covid-19 vaccine. Josie Adams reports on what this means for herd immunity, and for New Zealand’s strategy to fight the pandemic.
A new Stickybeak survey for The Spinoff of New Zealanders’ attitudes to the Covid crisis has found significant opposition to a hypothetical vaccine. Of the 605 respondents in the survey asked “if and when a Covid-19 vaccine becomes available will you aim to get vaccinated?”, 65% said “yes,” 20% said “unsure”, and 16% said “no”.
The poll results are weighted by age, gender and region to statistics from the 2018 Census.
Otago University professor Peter McIntyre, a member of the WHO Strategic Advisory Group of Experts (SAGE) on Immunisation, said those results were broadly in keeping with general attitudes toward vaccines – including those who are happy to receive them. “You see around 60-70% being unquestioning acceptors,” he said. “Unquestioning acceptors” are those who believe that if health experts and the government think a treatment is effective, they should be in favour too.
McIntyre says around 20-25% of people will have questions about the vaccine. Some will be easily satisfied by the answers they receive, and some will not.
Dr Nikki Turner, director of the University of Auckland-based Immunisation Advisory Centre, said around 20% of people are likely to be cautious about any new vaccine. “A Covid-19 vaccine would be a new vaccine, and many people may have doubts over its effectiveness and safety profile at this stage,” she said. “Their decision-making is likely to change either for the positive or the negative, based on the results of the science and then how the information on the final vaccine products are communicated.”
Public acceptance of a new vaccine would depend on how dangerous the virus is perceived to be, as well as the vaccine itself. Covid-19 is more likely to cause severe illness in the elderly, those with respiratory or heart conditions, and the immunocompromised. “People in contact with others fitting this description, along with those people themselves, would be pretty keen [on a vaccine],” said McIntyre. “I think we saw that just with this year’s flu vaccine uptake.”
This year nearly twice as many people opted for a seasonal flu jab as they did last year.
On vaccination and herd immunity, McIntyre said efficacy would depend on the characteristics of this currently hypothetical vaccine. “Provided the vaccine prevented all infections and not just developing severe symptoms if you are infected, then you could expect that 70% uptake or perhaps 60% would be enough to significantly dampen circulation of SARS-CoV2 [the virus causing Covid-19] based on what we know about how many people can catch the virus from one infected person.”
Turner said herd immunity would require a vaccine that stopped the virus living in the back of the nose and throat, and that the percentage coverage of the population required for herd immunity would depend on how well it does this. “Measles is extremely infectious, so to stop it spreading in a community requires around 95% of the population to be protected either by a vaccine or by previous immunity. In contrast, smallpox was less infectious so modelling suggested around 80% of the population needed to be immunised to stop it spreading.” Smallpox was eradicated worldwide in 1977.
Even lower down the scale, herd immunity can occur for Haemophilus influenzae (previously a common cause of bacterial meningitis in young children) with only a 50% vaccine uptake.
“The other problem with creating effective herd immunity levels is that groups who oppose vaccines often group together,” said Turner. “So there may be overall high coverage but localities of low coverage where the organism can still spread.” We’ve seen this with measles outbreaks, and then last year the unvaccinated group grew so large that we lost herd immunity.
Covid-19 belongs to a group of viruses that don’t necessarily imbue their survivors with lifelong immunity. Sars-CoV-1, the coronavirus behind the 2003/2004 Sars epidemic, left those who survived it with immunity for around two years.
In addition, viruses evolve into new strains; that’s why we get a flu shot every year. “If we presume for now that SARS-CoV2 is going to become part of the furniture over time, and if it will stay as virulent as it currently is, then yes it is quite possible that booster doses will be needed,” said McIntyre.
“Current evidence suggests that strains of SARS-CoV2 will change quite a bit less than flu does, but it is early days, and with wide circulation not just among humans but between humans and other animals, I’d say it’s still uncertain.”
Dr Caroline McElnay, director of public health, told The Spinoff New Zealand would maintain its elimination strategy in anticipation of an effective Covid-19 vaccine.
“For Covid-19 with a R0 around 2.5, we estimate about 60% vaccination rates would be needed to achieve herd immunity across the population,” she said. “But we would want to provide specific individual protection to key vulnerable groups (as we do for influenza) such as the elderly and people with underlying conditions as these are the groups most likely to have severe disease.”
The R0 is the average number of people who will catch the disease from a single infected person. For comparison, the 2009 H1N1 (swine flu) epidemic had an R0 of between 1.4-1.6. Measles has an R0 of between 12-18.
Turner doesn’t believe the results of the Stickybeak survey mean there is a strong anti-vaxx, or even anti-health sentiment in New Zealand. “Those who are currently opposed to a future Covid-19 vaccine or are unsure are not usually doing so because they are selfish,” she said. “Over the lockdown period the majority of New Zealanders have shown that they do care, and want not just to look after ourselves, but after each other.”
She’s more concerned about misinformation spreading to those who are unsure than of the small anti-vaxx population itself. “The answers must lie in us as a community really learning to look after each other and so creating a strong sense of trust in how we then chose to act jointly as a community – trust in our authorities and our science is earned, established and communicated effectively. I believe we have seen this happening over the lockdown.”
Respondents of the Stickybeak survey were self-selecting participants, recruited via Facebook and Instagram through ads targeted at 32 separate demographic sub-sets in New Zealand. A total of n=605 sample was achieved of adults in New Zealand.
Results are weighted by age, gender and region to statistics from the 2018 Census. For a random sample of this size and after accounting for weighting the maximum sampling error (using 95% confidence) is approximately ±4.8%.
The study went into the field on Monday 11 May and was completed Wednesday 13 May.
Stickybeak is a New Zealand startup launched globally last June, that uses chatbots to make quantitative market research more conversational and therefore less boring and even fun for respondents. Unlike conventional research which uses panels of professional paid responders, Stickybeak recruits unique respondents fresh for each survey via social media.
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