8 | New Scientist | 16 January 2021
IN A bid to vaccinate as many
people as fast as possible, the UK
is taking an unorthodox strategy
against covid-19. The country is
eking out its vaccine supply by
making most people wait three
months to get their second dose
of the two-shot regimen.
Both vaccines currently being
used in the UK were intended
to be given over much shorter
timescales. Changing a medicine’s
dosing schedule so dramatically is
unprecedented, and some experts
have branded it a dangerous
gamble, putting lives at risk.
But what does the evidence say?
The UK announced its approach
on 30 December as it was battling
a huge surge in covid-19 cases,
partly driven by a new, more
transmissible variant of the virus.
This was the same day that
the vaccine developed by the
University of Oxford and
AstraZeneca was approved,
and it was immediately
put on a timescale of up to
12 weeks between doses.
The UK government also
announced that the interval
between doses of the vaccine
developed by firms Pfizer and
BioNTech would be stretched
to the same duration. By then,
more than 600,000 people had
already been given their first
injection since the immunisation
drive began on 8 December.
Many scientists were shocked
by the move because it deviates
from the dosing schedules
intended in the vaccine trials:
three weeks for the Pfizer/
BioNTech vaccine and four
weeks for the one from
Oxford/AstraZeneca.
“A trial tells you that something
works, so why would you change
that?” says Stephen Griffin at
the University of Leeds, UK.
The approach makes most
sense for the Oxford/AstraZenecaAnalysisDOMINIC^
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IMAGESVaccine dosing controversy
Faced with surging covid-19 cases and a fast-spreading virus, the UK
has altered its vaccination strategy. Is that wise, asks Clare WilsonPeople wait for a covid-
shot at a vaccination
centre in Epsom, UKNews Coronavirus
such a major change to dosing.
The move to delay the second
shot was even more surprising for
the Pfizer/BioNTech vaccine, for
which all participants in the trials
got their second dose after about
three weeks. Pfizer and BioNTech
say that two doses of its vaccine
are required to provide the highest
protection against the disease.
There is some evidence to
support the change. In a letter
to doctors, the UK’s chief medical
officers said that the Pfizer/
BioNTech vaccine’s trial shows
a good level of protection
even before the second dose is
administered. The trial results
indicate that the efficacy was
89 per cent from 15 days after
the first dose. The vaccine has
been found to offer 95 per cent
protection from covid-19 overall,
after both doses are given.Data from a third vaccine,
developed by biotech firm
Moderna, showed a similar
response after one dose, lasting
for 15 weeks. The vaccine – like
the Pfizer/BioNTech one – uses
mRNA technology, and has been
authorised for use in the UK but
roll-out hasn’t yet begun.
The extended dosing schedule
is deemed necessary by the UK
government on public health
grounds. “The great majority of
the initial protection from clinical
disease is after the first dose of
vaccine,” the chief medical officers
said in the letter to doctors, adding
that immunising many people in
the next three months is better
than reaching half that number
with two doses to give only
slightly greater protection.
The only way that the longer
schedule would lead to more
deaths from covid-19 overall
is if the delay more than halves
the amount of immunity
provided by the first dose, which
is highly unlikely, says Stephen
Evans at the London School of
Hygiene & Tropical Medicine.
“The numbers are so obvious.”
There are wider considerations,
however. Leaving people with
only partial immunity to covid-
for many weeks could make the
virus more likely to evolve vaccine
resistance, England’s chief
medical officer Chris Whitty has
acknowledged, although he said it
was “quite a small worry”. On the
other hand, if vaccination roll-out
were slower, more people would be
exposed to infection, which also
raises the chance that the virus
evolves those critical mutations.
Another concern is that the
extended dosing schedule could
reduce the number of people whovaccine because its trial results
hint that it works better with a
longer wait between the doses.
Some people in the trials ended
up getting their second shot up
to 12 weeks after the first, and
the vaccine’s effectiveness at
preventing symptoms was 65 per
cent in this group, compared with
53 per cent in the rest.The numbers involved were
small, though, with only about
1800 people getting a delayed
second dose. The participants
also weren’t randomised to
the different schedules, so this
wouldn’t normally be seen as
good enough evidence to support“ We had to get over
ourselves and take
a pragmatic view.
We are in an emergency”