Science – Get ready for a boost

Vaccination is the only method that can lead to containment and eradication of the Covid-19 virus. However, an important new question now arises as the percentage of the New Zealand population who are fully vaccinated approaches 90 per cent. How long does immunity persist after the final jab? There have been a couple of recent scientific studies reporting the rate of decline – one four months and another six months after the second jab. A rough average of data from these two reports, one of which is in the top journal Nature, is that immunity from Pfizer vaccinations declines at a rate of about 5 per cent per month following the second jab.

This medium-term decline indicates that a third jab or booster is likely to be necessary within a year. It is even possible that an annual jab may prove necessary in the longer term. There is a strong drive for wealthy countries such as those in the EU and USA to expand the supply of boosters. But doing so is controversial, considering that some poorer countries have not yet received a single shot. The World Health Organisation appealed to the wealthy countries to hold off on boosters until a significant proportion of every country’s population has been vaccinated.

The term “jab” or “injection” may not be appropriate in future years, as both oral and nasal delivery methods of the vaccine are likely to become available in due course. The advantage of an oral vaccine is clear: it can be administered by the patient without the need to involve health professionals. This makes the administration of the vaccine much more accessible in poorer communities. An additional advantage of a nasal vaccine is that the virus population is highly concentrated in the upper respiratory system and so this direct delivery may have higher clinical efficacy than existing injection methods.

A supplementary line of development is also now appearing: the development of new antiviral drugs. These new pharmaceuticals are expected to play a valuable but limited role by reducing morbidity (serious illness and hospitalisation) and mortality (deaths) associated with Covid infection. These antivirals are being developed by Merck, Pfizer and Roche/Atea. Each operates differently. The Pfizer antiviral interferes with an enzyme that the virus needs to reproduce, and the Merck antiviral introduces errors into the genetic code of the virus.

Preliminary data suggests that the Pfizer antiviral may be somewhat more potent, but both are effective. An inherent risk in the global deployment of antivirals could be the development of resistance, as has happened with antibiotics. Antivirals are not a replacement for vaccination, but they will be a valuable supplementary agent. The New Zealand Government has signed up to receive 730,000 doses of one of the antivirals.

Optimistically, New Zealand is now approaching a final phase of the Covid-19 pandemic. At the completion of this phase, the pandemic is expected to become endemic, which means the community will learn how to co-exist with the coronavirus, just as we did many years ago with influenza.