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Delay in flu shot may not be a bad thing, but don’t miss out

26 June, 2018

Researchers at the Kirby Institute and UNSW Sydney have found that due to a decrease in the effectiveness of the flu vaccine over time, June and July could be the best time to get the jab for overall protection against the illness.

Research from the Kirby Institute at UNSW Sydney shows that due to waning in the effectiveness of the flu vaccine over time, getting the vaccine in June or July could be the best time for overall protection against the illness.

The research, presented earlier this month at the Public Health Association of Australia’s 16th Immunisation Conference in Adelaide, shows that getting the vaccine between March and August, the usual flu season, provides effective protection, however vaccinating in June-July at the peak of the season may prevent more cases of the contagious disease.

Vaccination is currently recommended as soon as the annual vaccine is available, which is usually March or April. But recent research suggests immunity from the jab may wane after three to four months. UNSW researchers used mathematical modelling to determine the ideal time to get the flu vaccine to ensure maximum immunity in Australia.

“Flu is an unpredictable virus. There are different strains every year, and the timing of the flu peak also varies from year to year,” says lead author Valentina Costantino, PhD student at the Kirby Institute at UNSW. “So our model looked at how flu has behaved in Australia for the last 10 years, and we used this to predict the average timing of the flu peak. We then modelled the waning of immunity to the vaccine, and found that vaccinating from June-July would provide slightly better protection.”

The model looked at people aged over 65 years, but the results hold true for all ages. Importantly, the results showed that for Australia as a whole, the difference between vaccinating in any month from March to August was not large. Vaccinating in any of these months prevents over 2000 cases a year, whereas vaccinating in June-July prevents up to 2461 cases in people aged over 65 years.

“Vaccination in March still offers reasonable protection to the population,” says Costantino. “But this study provides some preliminary evidence to suggest that getting the vaccine later in the flu season could provide slightly better overall protection.”

There have been concerns about delayed vaccination due to current shortage of flu vaccine. However the results of this study suggest that those who missed out on the vaccine in May are not disadvantaged.

“The data on waning immunity are based on only a few available studies, so there is still considerable uncertainty around this,” says Professor Raina MacIntyre, lead author and head of the Biosecurity program at the Kirby Institute and Professor of Infectious Diseases Epidemiology at UNSW. “For individuals at high risk for complications of flu, the decision to delay vaccination should be considered carefully and in consultation with their doctor. If there is a chance you will forget or miss your vaccination by delaying, it is much better to get vaccinated as soon as feasible. There is no evidence for being vaccinated more than once a year. The other caveat is that this study looked at the regular flu vaccine, but this year we have two enhanced vaccines for people over 65 years. There are no data on waning for these more potent vaccines.”

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